Filmmakers Brancaccio and Zeman walking near the ruins of Willowbrook.

When a group of friends and neighbors from Staten Island ventured into Manhattan last weekend to watch a hard-hitting crime documentary at the Tribeca Film Festival, most had no idea just how gutwrenching the experience would be.

It's been 22 years since a creepy drifter who lived in the woods behind the abandoned ruins of a mental institution was arrested for the kidnaping and murder of a 12-year-old girl with Down's syndrome — a horrific crime that soon took on a more ominous tone when the man, 43-year-old Andre Rand, became a suspect in the disappearances of several other Staten Island children over the years.

The strange case of Andre Rand and the still-missing kids remains one of the biggest mysteries in the annals of New York criminal history, and is now the subject of "Cropsey," a gripping documentary that debuted at this year's Tribeca fest.

But for the friends and neighbors of the victims who attended Saturday's screening, sitting through a rehashing of Rand's crimes — both real and imagined — was almost unbearably painful despite the passage of time.

"It was very emotional, and very sad," says Donna Cutugno, a neighbor of Jennifer Schweiger, the disabled girl who was abducted and killed in the summer of 1987 and whose body is still the only one that was ever found.

"You tend to put things in the back of your mind over the years, but seeing the film brought a lot of bad things back," adds Cutugno, who spearheaded the neighborhood search for Jennifer's body when the little girl went missing.

"It's still very painful because there has been no closure for my family," says Rita DiMartino, the aunt of Alice Periera, a 5-year-old girl whose disappearance in 1972 has been linked to Rand, though never proven.

"Alice's mother passed away without ever knowing what happened to her. But even though they focused more on (Jennifer), on the whole (the film makers) did a great job, because this is something that should be shown everywhere to build awareness that you can't trust people like (Rand)."

The case didn't only deeply affect those who lived in the close-knit, working-class neighborhoods of Richmond and New Dorp, where at least three other children besides Jennifer and Alice were presumably abducted since the early 1970s. It touched the filmmakers, too.

Like most every kid growing up on Staten Island at the time, "Cropsey" co-directors Joshua Zeman and Barbara Brancaccio were well-versed in the details of the crimes. But what spurred them to make the film was how Rand's arrest in 1987 turned folklore into fact.

Rand, who had already served time for sexually abusing a Bronx girl in 1969, put a sinister face to one of New York's most enduring urban legends: The twisted tale of Cropsey, an axe-wielding maniac who lived in the woods and whose gory exploits were the subject of many a scary campfire tale.

Except that the Staten Island version had Cropsey being a mental patient who had escaped from Willowbrook, the massive state facility that was shuttered in the 1970s.

For Zeman and Brancaccio, Rand was the embodiment of their childhood Boogeyman. He had worked at Willowbrook for two years in the late 1960's, and after the facility was shut, he had lived in makeshift campsites in the thick forest of the Willowbrook grounds.

Filmmakers Brancaccio and Zeman walking near the ruins of Willowbrook.

"We didn't know each other as kids, but we both knew about Rand and we both grew up with the cautionary tales of not going into the buildings and the woods around Willowbrook because of Cropsey," says Zeman, 37.

"When Rand was being re-indicted in 2000 for the disappearance of one of the children, we took this as a sign," adds Zeman. "So we picked up a camera and started shooting. We couldn't believe this story had never been told before."

"Cropsey," which has a final screening on Saturday at 8:30 pm at AMC Village 7, unfolds like a eerie episode of "CSI: Staten Island." Zeman and Brancaccio not only went to great lengths to interview victims' relatives, neighbors, witnesses and the cops who worked the missing children cases, they also bring their camera into the deserted buildings, underground tunnel networks and wooded areas around Willowbrook, where most people believe Rand's alleged victims are buried.

"It's unsettling to be there by day," says Branaccio, 38. "But it's even scarier at night. Walking through the rooms, it still has that mental institution feel. You can still see the hospital beds and tables, and part of the horror is knowing something bad happened there."

The co-directors didn't merely retell the story and revisit the crime scenes, however. They also played amateur sleuths — though Rand was twice convicted for the kidnaping of two of the children (but not the murders) there are still those who think he may not have had a hand in the other disappearances.

During the making of the film, they even managed to start corresponding with Rand, who sent them vast amounts of letters from Sing Sing professing his innocence, hoping to get the truth.

"When you're receiving that many letters and so many details, you want to find the clues," says Brancaccio.

There have also been whispers that a Satanic cult may have been reponsible for at least some of the abductions, which most people familiar with the case strongly discount.

"There have been all sorts of rumors about devil worship, but we never found anything to substantiate that," says Robert Jensen, a retired detective who worked the case.

Yet the biggest mystery that remains isn't who did it, but what he did with the bodies.

"The fact that no one's been missing for the 22 years since Andre Rand has been in prison means he is definitely the person responsible for the missing children," says Cutugno, who helped found Friends of Jennifer for Missing Children, whose goal is to get Rand, now 65, to reveal where the bodies are buried.

"The one regret about the case is that we didn't find that out," says Jensen. "It would give a closure to all the families."